Torque-limiting tool holder for machine tools



Oct. 28, 1958 L, PRAS 2,857,793

TORQUELIMITING TOOL HOLDER FOR MACHINE TOOLS Filed June 1, 1956 United States Patent TORQUE-LIMIIING TOOL HOLDER FOR" MACHINE TOOLS Lucien Pras, Billancourt, France, assignor to Regie National des Usines Renault, Billancourt, France, a French works Application June 1, 1956, Serial No. 588,691

Claims priority, application France June 8, 1955 I 8 Claims. (Cl. 8152.4)

This invention relates to tool holders and more particularly to' a torque-responsive tool holder. When a rotary cutting tool, `such as a drill, tap, milling cutter, etc., is used on a machine tool, the following disadvantage is often found to occur: the force required to drive the tool in rotational movement may suddenly increase owing to a chip becoming jammed, or owing to wear on the tool or for some other reason, and this results in the breaking of the tool, which is rigidly connected to the spindle of the machine.

The invention relates to a tool holder which makes it possible to eliminate this danger of the tools breaking. According to the invention, the cutting tool is carried by a` nose piece driven by a tool holder shank fast with the spindle of the machine, the shank and the nose piece being connected together by means of balls which t into holes in a perforated plate, the force exerted on these balls being adjustable. When the resistant torque exceeds a limiting value, the said balls are moved out of their holes and the tool and its nose piece are immobilised. Moreover, the tool carrier is equipped with an indicating device which comprises a control element which is displaced radially when the driving balls move out of their housing holes.

A torque-limiting tool holder, intended more particularly for driving a tap, will now be described by way of non-limitative example, with reference to the accompanying drawings, wherein:

Fig. 1 is a vertical sectional view of the tool holder in the normal driving position;

Fig. 2 is a plan view in section of the spring-carrying ring;

Fig; 3 is a plan view of the cam locking device;

Fig. 4 is a vertical sectional view of the central part of the tool holder, in the de-clutched position.

The shank 2 of the torque-limiting tool holder is introduced into the hollow spindle 1 of the machine. The said shank is immobilised with respect to the spindle by a bolt 3 carried by the said spindle. The position of the shank 2 in -the longitudinal direction is determined by a nut 4 and a lock nut 5. The nut 4 carries studs such as 6 which penetrate into corresponding notches provided in the end of the spindle.

The lowerend of the shank 2 is hollow and its outer surface is smooth. Arranged on the shank are an adjusting nut 8a washer 9, a spring-carrying ring 10 and a washer 11. y

The spring-carrying ring 10 is illustrated in sectional view in Fig. 1, and in plan view in Fig. 2. Fo-rmed in the lower'portion of the said ring are the equidistant blind holes 12, to the number of twelve, for example (Fig. l). A spring 13 is mounted in each of these holes. Slidable above the ring 10 is a cam 14 comprising a split collar whosetwo parallel faces 15 and 16 (Fig. 2) are guided by corresponding surfaces of the ring 10. The latter comprises also two housings 17 and 18, each of which contains a compression spring, 19 and 20, respectively, which tend to urge a portion of the cam in a radial outward direction.

The ring 10 is surrounded by a sleeve 21 or cam lockingdevice which, in the position illustrated in Fig. 1,

prevents any radial displacement of the cam 14. Thesaid cam locking device'bears `against the washer 11.

and, as Fig. 3 shows, carries two small bars 22 and 22a which in turn carrytwo springs ,23' and 24 whose free ends abut against theA washer 9".(Fig. 1). The nut 8 comprises a plurality of tapped radial holes 25, in such manner that the said nut is adapted to be fixedv in oneof several positions by means of a screw 26 extending through one of the said tappedy holes and abutting 4against the end of a recess such as 27 which is formed in they shank 2.

Mounted in the hollow end of the shank 2 is a nose piece 28 whose head 29 carries the working tool a tap, for example. The nose'piece carries a plate 30 which is formed with a certain/number of holes such as 31, which are distributed over thewhole periphery of the said plate. The latter is surroundedby a sleeve 33 which forms the end of thev shank 2 and whose top end comprises a number of holes correspondingin number tov the holes in the plate 30. Balls such as 34 are mounted in the holes of the sleeve,`lthe diameter of the said holes being larger than that oflthe balls so that the latter can rotate freely relatively to the said holes. 'On the other hand, the holes such as 31 formed in the plate are of smaller diameter than the diameter of the balls, so that the latter can only penetrate partially therein.l v

The perforated plate or collar 30 is rendered fast with the nose piece 28 by two keys 36 and 37 which are held by a supporting ring 38. Situated between this ring and the tool holder head 29y is a compression spring 39. '"lhe perforated plate 30 also bears against a ring 40 compr1smg a certain number of orifices which are arranged concen- 'trically about the axis of they apparatus, and each of which contains a ball such as 41, the said balls being in contact with the supporting ringl 38. 'The oriiices of the ring 40 are slightly smoothed at ktheir ends which face towards theaxis 'of the apparatus,whilst the balls are prevented from escaping from their housings by an elastic ring 43 surv rounding the ring 40. Finally, the ring 40 contaimng the i balls is held in position by an elastic ring 44 which, at the time of assembly, is inserted into an annular groove 45 formed in the end of the sleeve 3.3.

The tool holder operates in'the following manner: The spindle 1 of the machine is driven in rotational movement and the tool holder assembly rotates withr the said spindle. In fact, with the nut 8 appropriately adjusted by means of the various holes adapted to receive the screw 26, the distance between the washer'9 and the perforated plate 30 is such that the springs 13 are compressed and the balls 34 are stronglythrust into the holes such as 31 provided in the perforated plate 30. Thus the said balls become locked and transmita driving torque between the shank 2 and the perforated plate 30, i. e. between the shank 2 and the nose piece 28 which is secured to the perforated plate 30. f When the driven tap encounters an obstacle which might cause the tool to break, the resistant or counter torque exceeds a predetermined limit-value determined by the position of the nut 8 and the force of the springs 13. The balls 34 are then expelled from the holes such as 31, and the lower part of the device, constituted by the tool, the nose piece 28, the keys 36 and 37, the perforated plate 30 and the supporting ring 38, is declutched and thus no longer rotates. The rest of the apparatus continues to rotate with the spindle 1. However, the spindle of the machine continues to advance and the whole of the apparatus continues to be displaced axially,

except for the tool and the nose piece 28, which are im 3 mobilisecl.A The axial"di'splaeement is permitted by the compression of`the' spring"39"an'd"by"the keys 36 and 37 sliding in their grooves 46 and`r 47.

Furthermore, when the balls 34 are expelled `from the perforated" plate 30, 'the v'washerl' and the cam locking device 21 are raised. The bent-over 'upperedge 48 of the cam locking device'then occupies the position illustrated in Fig. 4 and,l allows the cam 14ml toescape in the radial direction; The movement of this cam can be used to operate asign'al, and'canrthus bring about the stoppage of the spindle 1. In the constructional example illustrated inthe drawings, the cam 14`actuates an` electric switch by means offafinger which is shown diagrammatically atf49.

Iclaim:

1,. A toolA holdercomprising, a.rotatable drivingmember, a driven member coaxial-therewith andhaving means for holding a tool, a torque-controlled axial clutch for coupling said driving4 anddrivemmembers and .for uncouplingthemwhen va-predetermined-value of countertorque is applied to `the drivenA member, comprising; means fixed tosaid driven,member defining a plurality of spaced indentations concentric` with-the longitudinal axis of said members, aA` plurality ofspherical members equal in` numbernto said-indentations, means fixed to the driving member for normally retaining said spherical members in` individual alignment with said indentations and adaptedto allow the-spherical members to move in opposite,V directions axially oflthe tool holdereach of said; indentations being adapted to receive a portion of an individualsphericalV memberand cooperate therewith in releasably coupling the-driving and; driven members, means including rneansdisplaceablegaxially on the tool holder for adjustablyrapplyinga pressure -on said spherical members andincludingresilient means-cooperating withsaidlast mentionedmean'sfor normally biasing the spherical membersin a direction axially of the tool holder and toward engaging. theuindentations,.to releasably couple the driving-anddriven members, cam means normally biased in a direction radially outwardly of 'the tool holder for indicating 4when'saidzpredetermined value of countertorque is reached andlfor initiating: theV stopping of saidV driving memberwhenrsaid predetermined `value ofcountertorque obtains, the'axially displaceable pressure-applying means having meansl normally-holding=saidA cam means in aA locked-position andarr'anged to-release said cam means whendisplaced`4 axially in)` a'Ad-irection. opposite to the direction -in which sidcoupling pressure: is --normallyr applied to said spherical members, whereby-whenacounter-torque* corresponding@ to saidipredet'ermined' countertorque-is' appliedltcvsaidv driven-membersaid means' defining theindentationsf isangularly-displaced relative the means normally retainingthe spherical-membersin alignment with `saidfindentations,therebyA moving thel spherical members axially ina direction for disengagingA them from saidvindentations soas to uncouple-the-drivingand driven'` members: and `said pressure applying; means `is displaced in the cam-releasing..direction.-

2. Aztool.holder.accordingto--claiml 1 in.` which said means Afor applyinglsaid biasing pressure on the. spherical members 4comprises .ani-annular. member disposed overlylng said spherical members, circumferentiallyaround sa1,ddr1v1ng memberand movableaxiallyof the driving member, and u in whichtsaid resilient 4means ,comprise ar plurality. of 4spaced springswdisposedA substantially concentrically about the axis of said driven member and biasing said' annular memberinto constant contact willi'said spherical members.

3. A tool holder according to claim 1, including means to adjustably compress the springs thereby to selectively control the value of thecounter-torque at which said driving and driven members are uncoupled.`

4. A tool holder accordingtoiclaimf 1, in which said means for normally retaining said spherical members individually aligned with the individualindentations com$` ond `sleeve fixed Ato-Said drivingmember in which saidt` drivenrmember isA disposedaxially thereof, said means` defining the indentations comprising'4 an, annular `collar` fixed to said driven member rotatably mountedsinternal-` ly of said second sleeve, means for fixing thefcollar to` the driven member for rotation therewith, said driven` member being` provided with angularly` spaced guide means cooperating with said last mentioned means for selectively allowing` the driven member to move.axially of the clutch and thedriving-member.

6. A-tool holder according'to claim 5, ncluding=resili ent means cooperating with said second sleevetolmain-` tain said driven member in a predetermined extended position relative to the driving-member.

7. A tool holder according toclaim 6,.inwhich saidf resilient means comprises a.compression-spring;disposed circumferentially around said driven member; andl isarranged to allow the driven rrxembelto4 befselectively displaced axially` ofthe clutch andfdrivingrmember.,

8. A tool holderaccording to claim 1, infwhich said cam means comprises a splitcollar havinglgazfirstportion fixed on said driving member for rotationotherewitlr` and a second portion constantlyi biased. innazdirection radiallyof thedriving member; andiresilientnmeansconstantly biasing.l the. second portion im said.` radiali direction.

References Cited in the fileiofthis-patent-I UNITED STATES PATENTSl 1,657,274 Niedhammer: Jan: 24, 1928 1,672,964 Stull June 12,- 1928 1,881,633 Johnson Oct.` ll, 1932 1,883,164 Vassakos; .Oct; 18, 1932 2,182,627 Gauld.- ,Dec. 5, Y1939 2,263,709 Van Sittcrt Nov. 25, 19,41l 2,293,786 Worden Aug, 25, 1942 2,342,540 Hale Feb. 22, 1944 2,396,040 Darling Mar. 5, 1946 2,728,579 Djidch Dec. 27, 1955 2,732,746 Livermont Jan. 31,v 1956. 2,786,377 Riess Mar. 26,y 1957 FOREIGN PATENTS 697,021 Great Britain sept. 16, 1953 846,203 France May 27, 1939 

